1. Field of the Invention
The present invention relates to a toroidal-type continuously variable transmission which is used, for example, as an automatic transmission for a vehicle and, in particular, to such toroidal-type continuously variable transmission which is enhanced in the durability of its component parts such as disks and power rollers.
2. Description of the Related Art
Conventionally, as a toroidal-type continuously variable transmission, there is known a toroidal-type continuously variable transmission having such a structure as shown in FIG. 1.
Within a housing (not shown), specifically, on an input shaft 3 rotatably supported in the interior of the housing, there are disposed an input side disk 1 and an output side disk 2 in such a manner that they are concentric with and opposed to each other. The input shaft 3 is penetrated through the axial core portion of a toroidal transmission part including the input side disk 1 and output side disk 2. A loading cam 4 is disposed on one end of the input shaft 3. This loading cam 4 is structured such that it can transmit the power (rotational force) of the input shaft 3 to the input side disk 1 through a cam roller 5. Referring in more detail to the structures of the input side and output side disks 1 and 2, they respectively include inner surfaces formed as concave surfaces each having an arc-shaped section, have substantially the same shape, and are disposed concentric with each other with their respective inner surfaces opposed to each other. These mutually opposed surfaces are respectively formed as toroidal surfaces such that they cooperate together in forming a substantially semicircular shape, when the present toroidal-type continuously variable transmission is viewed as a section in the axial direction thereof.
Within a toroidal cavity defined by the toroidal surfaces of the input side and output side disks 1 and 2, there are disposed a pair of power roller bearings 6 and 7 which are respectively thrust rolling bearings, in such a manner that they are in contact with the input side and output side disks 1 and 2. By the way, the power roller bearing 6 is composed of a power roller 6a (which corresponds to an inner race forming the power roller bearing 6) which can roll on the toroidal surfaces of the input side and output side disks 1 and 2, an outer race 6b, and a plurality of rolling bodies (steel balls) 6c. On the other hand, the power roller bearing 7 is composed of a power roller 7a (which corresponds to an inner race forming the power roller bearing 7) which can roll on the toroidal surfaces of the input side and output side disks 1 and 2, an outer race 7b, and a plurality of rolling bodies (steel balls) 7c; and, the power roller bearing 7 is used to support a thrust load that is applied to the power roller.
That is, the power roller 6a also plays the role of an inner race which is a component of the power roller bearing 6, while the power roller 7a also plays the role of an inner race which is a component of the power roller bearing 7. In the present structure, the power roller 6a is pivotally and rotatably mounted through a pivot shaft 8, the outer race 6b and the plurality of rolling bodies 6c on a trunnion 10 swinging about a pivot shaft 9 disposed at a position which is perpendicular to an axial line of the input shaft 3 and does not intersect the axial line thereof (hereinafter, this physical relationship is referred as xe2x80x9ca torsional positionxe2x80x9d). And, at the same time, the power roller 6a includes a peripheral surface formed as a spherical-shaped convex surface, and is inclinedly supported about displacement shafts 0, which are respectively supported on their associated trunnions and serve as the centers of the toroidal surfaces of the input side and output side disks 1 and 2. On the other hand, the power roller 7a is pivotally and rotatably mounted through a pivot shaft 9, the outer race 7b and the plurality of rolling bodies (steel balls) 7c on a trunnion 11 swinging about a pivot shaft 9 disposed at the torsional position with respect to the input shaft 3; and, at the same time, the power roller 7a is inclinedly supported about displacement shafts 0, which respectively serve as the centers of the toroidal surfaces of the input side and output side disks 1 and 2. And, these power rollers 6a and 7a transmit the power of the input shaft 3 to the input side and output side disks 1 and 2.
By the way, the input side and output side disks 1 and 2 are independent from the input shaft 3 with needle rollers 12 between them (that is, they are held in such a state where they are not directly influenced by the power of the input shaft 3). On the output disk 2, there is disposed an output shaft 14 which is arranged in parallel to the input shaft 3 and is also rotatably supported on the housing (not shown) through angular bearings 13. In the present toroidal-type continuously variable transmission 20, the power of the input shaft 3 is transmitted to the loading cam 4. And, in case where the loading cam 4 is rotated due to such power transmission to the loading cam 4, power caused by the rotation of the loading cam 4 is transmitted through the cam roller 5 to the input side disk 1, so that the input side disk 1 can be rotated. Further, power generated due to the rotation of the input side disk 1 is transmitted through the power rollers 6a and 7a to the output side disk 2. As a result of this, the output side disk 2 can be rotated integrally with the output shaft 14.
In transmission, the trunnions 10 and 11 are respectively moved by a slight distance in the directions of the displacement shafts 0. That is, the axial-direction movements of the trunnions 10 and 11 shift slightly the intersection between the rotary shafts of the power rollers 6a, 7a and the axes of the input side and output side disks 1 and 2. This intersection shift loses balance between the rotational peripheral speed of the power rollers 6a, 7a and the rotational peripheral speed of the input side disk 1; and, due to the component of the rotation driving force of the input side disk 1, the power rollers 6a, 7a are caused to roll inclinedly around the displacement shafts 0. Therefore, the power rollers 6a, 7a are allowed to roll inclinedly on the curved surfaces of the input side and output side disks 1 and 2. As a result of this, the speed ratio is changed: that is, deceleration or acceleration is carried out.
As a toroidal-type continuously variable transmission having the above structure, for example, there is known a conventional toroidal-type continuously variable transmission which is disclosed in JP-B-2-49411U. And, as the input side disk, output side disk and power roller bearings of the above type, as set forth in [NASA Technical note NASA ATN D-8362], there are conventionally known input side disk, output side disk and power roller bearing which use AISI52100 (JIS SUJ2, corresponding to high-carbon chromium bearing steel); and, as disclosed in JP-A-9-79336, there are known disks and bearings in which SCM420, that is, steel for mechanical structural purposes containing Cr is carbonitrided.
In the above-mentioned conventional toroidal-type continuously variable transmission, when it is driven, there are generated high contact pressures respectively between the input side disk and power roller bearings, between the output side disk and power roller bearings, and between the power roller inner and outer races and rolling bodies. These high contact pressures are combined with lubricating oil (traction oil) existing between the input side and output side disks and power roller bearings, and between the power roller raceway surfaces and rolling bodies to lower the fatigue lives of the contact surfaces. Therefore, for the purpose of enhancing the rolling fatigue life under the high contact surface pressure and high temperature conditions, conventionally, the input side and output side disks as well as the inner races or outer races of the power roller bearings are carburized or carbonitrided to thereby prevent the high temperature strength of the surfaces thereof from lowering. Also, in order to extend the lives of the disks and power roller bearings, as disclosed in U.S. Pat. No. 5,735,769, JP-A-10-231908, and U.S. Pat. No. 6,066,068, conventionally, the rolling surfaces of them are treated by shot peening to thereby apply residual compressive stresses to them, with the result that the lives of the disks and power roller bearings can be effectively extended.
However, the above-mentioned measures are mainly the rolling fatigue measures when foreign substances such as iron powder are not mixed in the lubricating oil. In the actual toroidal-type continuously variable transmission, iron powder, which stuck to a gear when the toroidal-type continuously variable transmission was manufactured, is mixed into the lubricating oil, and such iron powder is bitten into the contact portions between the disks and power rollers to thereby cause impressions in the disk rolling portions and power roller rolling portions; and, the peripheries around these impressions provide stress concentration areas and, therefore, there can be occurred cracks in these areas, to thereby generate the flaking.
As a measure against the shortened life caused by the biting of the foreign substances, conventionally, there is taken a measure in which the quantity of retained austenite is increased to thereby relieve the stresses in the peripheries around the impressions. However, in the portion subjected to shot-peening, the retained austenite is reduced in quantity due to the transformation of the processing induced martensite, that is, the quantities of retained austenite in such shot-peening portions are below the retained austenite 15% in which a life extension effect can be obtained. Therefore, the shot peening, which was enforced for the purpose of enhancement in the lives of the foreign-substance-bitten portions, results in that the foreign-substance-bitten portions are flaked to thereby shorten the lives thereof.
The invention aims at eliminating the drawbacks found in the above-mentioned conventional toroidal-type continuously variable transmission. Accordingly, it is an object of the invention to provide a toroidal-type continuously variable transmission in which at least one of the concave surface of an input side disk, the concave surface of an output side disk, the convex surfaces of power rollers, the raceway surfaces of the inner races of power roller bearings, and the raceway surfaces of outer races of power roller bearings are, after heat treatment, ground, superfinished, subjected to shot-peening, and superfinished again to provide the surface residual compressive stresses in the range from xe2x88x92780 to xe2x88x921800 MPa, thereby being able to obtain a good life extension effect when compared with the conventional toroidal-type continuously variable transmission.
Also, it is a second object of the invention to provide a toroidal-type continuously variable transmission which, by providing the surface retained austenite of 15% or more, can obtain a good life extension effect with respect to the flaking caused by the biting of foreign substances.
Further, it is a third object of the invention to provide a toroidal-type continuously variable transmission which,in the depth of 50 xcexcm from the surface, by providing the retained austenite of 20% or more, can greatly extend the lives of the components thereof with respect to the flaking caused by the biting of foreign substances.
In attaining the above objects, according to a first aspect of the invention, there is provided a toroidal-type continuously variable transmission, including:
an input shaft supported so as to be freely rotatable;
an input side disk rotatable together with the input shaft and including an inner surface formed as a concave surface having an arc-shaped section;
an output side disk including an inner surface formed as a concave surface having an arc-shaped section, the output side disk being disposed concentrically with the input side disk in such a manner that the inner surface thereof is opposite to the inner surface of the input side disk;
a plurality of trunnions respectively swingable about their associated pivot shafts disposed at tortional positions with respect to the input shaft;
a plurality of displacement shafts respectively supported on the trunnions;
a plurality of power rollers each including a peripheral surface formed as a spherical-shaped convex surface, disposed on the inner surfaces of the trunnions, and rotatably supported in the peripheries of the displacement shafts while the power rollers are held by and between the input side and output side disks; and,
thrust rolling bearings for supporting thrust loads applied to the power rollers, each of the thrust rolling bearings including:
an inner race raceway formed in the outer peripheral surface of the power roller; and
an outer race disposed inside the trunnion and having an outer race raceway,
wherein at least one of the concave surface of the input side disk, the concave surface of the output side disk, the convex surfaces of the power rollers, the inner race raceways and the outer race raceways of the thrust rolling bearings, after heat treatment, subjected to grinding, superfinishing, shot-peening, and superfinishing again in this order, and the value of the resultant surface residual compression stress is in the range from xe2x88x92780 to xe2x88x921800 MPa.
Also, according to a second aspect of the invention, in the toroidal-type continuously variable transmission as set forth in the first aspect of the invention, at least one of the concave surface of the input side disk, the concave surface of the output side disk, the convex surfaces of the power rollers, the inner race raceways and the outer race raceways of the thrust rolling bearings is, after heat treatment, subjected to grinding, superfinishing, shot-peening, and superfinishing again in this order, and the value of the resultant surface residual compression stress is in the range from xe2x88x92780 to xe2x88x921800 MPa and the quantity of the resultant retained austenite is 15% or more.
Further, according to a third aspect of the invention, in the toroidal-type continuously variable transmission as set forth in the first aspect of the invention, at least one of the concave surface of the input side disk, the concave surface of the output side disk, the convex surfaces of the power rollers, the inner race raceways and the outer race raceways of the thrust rolling bearings is, after heat treatment, subjected to grinding, superfinishing, shot-peening, and superfinishing again in this order, and the value of the resultant surface residual compression stresses is in the range from xe2x88x92780 to xe2x88x921800 MPa, the quantity of the resultant retained austenite is 15% or more, and the quantity of the resultant retained austenite in the depth of 50 xcexcm from the surface is 20% or more.